Written for a Prompt:

What if upon his death in the Red Wedding Robb is ISOTed to the first day of the Starks' arrival in King's Landing, but in an alternate continuity where all 5 children of Ned & Catelyn were born of the opposite gender than they were in the canon?

Letter 1 - Robb

Dear Jon,

I don't know why I'm writing you this letter; I doubt it will ever get to you - the real you, not the doppelgängers of this world. Perhaps if I knew how I ended up here, but the last thing I remember from our world is dying at the hands of Roose Bolton. I doubt the man himself could have done this, even though he would probably want to just to make my failure worse. Or for that matter the Freys.

You're the only one of us who isn't massively changed in this place, your copy still being male and still joining the Night's Watch. I'm afraid your relationship with mother was even worse though, apparently brought on by my 'differences'. Theon's with you at the Wall apparently, having been forced to join after he revealed himself to be a jackass earlier than in our world. I hope his cock falls off while he's there. Which is assuming your double or Benjen's hasn't shoved him off the top yet.

Unfortunately the rest of our siblings haven't been so lucky. Sansa is now an arrogant swine called Sandor, even more obsessed with the south than she was back home. Even more disturbingly, he still fawns over Joffrey and according to my doppelgänger's memories, desires to be a member of the Kingsguard. Which is worrying considering he's the heir to Winterfell. I plan to try and shove him onto the intelligent path but apparently none of our clones's previous attempts have worked.

Arya (or Arry) seems to have come out on this side a bit better. Worships you, of course and dreams of joining the Night's Watch. He might be mother's favourite in this world, finally a child that looked like father, a son no less.

Bran (or Brienne) was still crippled here. She and Roslin (aka Rickon) stayed back home with Arry. I only hope the assassin doesn't manage to make it through to them without me there.

And as for me, well this letter is being sent to you by the future queen of Westeros. My clone was no exception to the sudden sex change, with my mind now being stuck inside the body of Lady Robyn Stark, betrothed of Prince Joffrey Baratheon.

Yes, you heard that right.

I just hope I can poison the shit at some point because I'm not sure how else I'm going to get out of here. I don't even care if the Lannister's steal the throne, I just don't want father's murderer on top of me! It doesn't help that none of my sword skills have come over, Robyn's mind being cluttered with sewing and dancing. Though at least she seems to have hated both of those, lending her attention more to politics- which I admit were what knocked me over in the end.

I have to leave now - father has asked me to accompany him to the tourney - but I will write again soon if I can. It's the only thing keeping me sane at this point. If you do get this letter - try to find Sansa and Arya and protect them. You're the only family they'll have left now. Tell them how sorry I am for failing them.

Your brother, Robb

Letter 2 - Jon

Robb,

I...seven hells, how are you alive? And in another world to boot? Robb, I can barely believe it but your letter did appear in front of me, by no mundane means. Could the gods have done this for you as a reward? A life taken under Guest Right given back? But why not send you to this world, instead of one where you're a woman?

I'm afraid things have not been going well on this side either brother. Your army collapsed after the Red Wedding - that's what they call Bolton's Betrayal now - and the Lannisters and their friends swept in to pick up the leftovers. Roose Bolton's army is heading home through the neck I imagine, according to the news here he's been given Winterfell and father's old titles. There aren't enough Northerners willing to fight him for him to be stopped.

I can't leave the Night's Watch now to help them in their fight; no matter how much I wish to. I tried leaving when you first called the banners and was only brought back by my friends crying on about honour - though considering I hadn't taken my oaths, I...oh Robb, I should have been with you; even if we both died. Screw my honour, I should have been helping you save our siblings. I could have warned you about Theon or the Karstarks or the Westerlings. I could have convinced you not to break the pact with the Freys!

I don't know what to tell you.

But you should know, apparently Bran at least survived Theon's attack on Winterfell. I don't know how he managed it, but my friend Sam found him Beyond the Wall with the two Reed children. The problem is Sam didn't bring him back to the Wall and let him carry on. I'm keeping scouts on the lookout, but with the Free Folk massing to attack the North, there isn't much chance that we'll find him first.

Robb, you have to keep these letters secret. Burn them if necessary, but you can't let the people in that world find out what you're planning. I'm not saying don't kill Joffrey - do, the shit deserves it - but be stealthy. Getting caught will only end with you dying again and who knows if you'll even come back this time? Work from the shadows, follow the Queen's example. You need to be above suspicion. You need to be Joffrey's loving betrothed who could never bear to murder him.

It will be hard, I know. Sansa/Sandor from what you said will be difficult. Try to appeal to his pride and any sense of duty, he has to have one if father raised him anything like you and me.

I still miss you,
Jon

Letter 3 - Robb

Jon,

Sandor (our brother, not the Hound) is a complete ass! Can you believe it, I accidentally manage to poke myself with the needle while doing sewing work and he immediately starts going on about 'embarrassing our house'. If he insults me again I'll show him embarrassing our house! I was tempted to punch the little shit, whose been an absolute arsehole ever since we arrived in King's Landing - I mean, since I was transporting here. As it happens, I threatened to convince father to send him home. That shut him up!

Maybe my mood would be better if I wasn't stuck in the middle of my moonblood, having to deal with all the cramps and stabbing pain that annoys mother so much. I wonder if our Sansa has had to deal with this yet? I'm not entirely sure if I would wish it on her because believe me, my arse is in agony! Even Robyn's memories going on about this being 'normal' aren't helping because sorry; there is blood coming out of my ass and there's nothing I can do about it!

At least politics has been going better for me here, though all things considered that's not saying much. The Queen despises me for whatever reason, even though I've been forced to be nothing but polite. Maybe she's pissed that someone other than her is marrying her son - I wouldn't put it past the cunt. And yes, she's definitely fucking her brother here as well. I see those looks they're giving each other! She better hope she's never locked in a room alone with me or I might just strangle her to death!

I'm the darling of the rest of the court however, 'Prince Joffrey's beautiful bride to be'. Suck-ups. They're hoping I don't notice their comments about 'my beauty being smothered in the North' or similar nonsense. All of the ladies are either Cersei's dogs or half-witted Crownlander wives attracted to the capital. I've held my tongue around them - for father's sake more than anything - but if I had Dacey's mace...

I've started doing an Arya, hanging around with the servants. They're so much less irritating than the court, sensible and less obsessed with appearances or niceties and besides which - if we need to get out of the city quickly it would be good to have them on our side: though Sandor will probably insist on staying. And I'll need their allegiance if...Robyn is meant to marry Joffrey at the end of the month.

And I've got no idea how to pull out of it. I've made no secret of my dislike for the prince to our father, but his friendship with the King has blinded him to how frankly terrified I am! I don't know what to do; I can't stab him to death in his sleep, I can't poison him, I can't get Sandor to cause an incident! I've got my skill for tactics and Robyn's for politics but nothing will help! If this was a battlefield I'd know what to do but I'm stuck in this stupid body, forced to participate in duties that were never mine in the first place!

I don't know what to do Jon. I...I need you here with me. Help me.

Robb

Letter 4 - Robyn

Brother,

You don't need to worry about me. I'm fine, I can look after myself. The little shit is easy to train, once you've learnt how.

So I haven't used the dagger you enclosed in your last letter. The boy is no threat to me now, not after I've discovered a secret that even he didn't know about himself. For you see, while the pain of others will bring him a perverse joy - as we suspected - so too will his own. A few slaps of the whip and he's clay in my hands, mortar to shape as I see fit. In return for the simple honour to worship his Queen, he will do anything to please me. And to get myself through it, I just have to think of all of you safe.

I failed at that in our world, I won't fail here.

But moving on from Joffrey, regarding your situation with Stannis and his Red Woman. You should accept his offer. I've no love for Stannis - mother was convinced he was a kinslayer - but he is a thousand times better for the north than Roose Bolton and his bastard. You would be a thousand times better than either of them and - if you can find Maege Mormont - I appointed you my heir. Sansa is the Lannister's key to the North. Bran is missing. Arya and Rickon are dead.

You're the only one of us who's free now.

I know you're worried about the Watch. From what you've said through our letters the situation up there is terrible. But the Watch needs a strong North behind it in its dilapidated state and only you can do this.

Being a lord is hard and being a king is harder. But you have to try Jon. Try and succeed where I failed. Force Stannis to accept the terms of Sansa and Arya (if by any chance she's alive) being returned to you unharmed and to keep his Red Woman away from the godswoods. If you have to, take the Wildling Princess you've mentioned as a wife. Bind our kingdom back together against all our enemies. Both inside and out.

And I will be with you all the way Jon. Any worries you have will be my worries. Any fears or any doubts. But you need to trust me.

I'm sending you something, enclosed in this letter. It...took me a while to make but, it should bring you comfort. Our family, united in needlework even though unimaginable distances separate us now. All of us.

We are Starks Jon, and Starks do their duty. No matter the cost.

Robyn Baratheon

Letter 5 - Jon

Robyn,

The Boltons are dead. Winterfell is ours once more, thanks to your plan. And as I write, Rickon is being fetched from Skagos - of all places Skagos? - where House Manderly had been hiding him.

Yes, Rickon is alive! And apparently completely unharmed! I would call it a miracle if not for everything else that has happened. Apparently a Wildling woman was somehow sheltering him, though I have no idea how that happened.

I've already announced to Stannis that I consider Rickon's claim to come first, even if I have been legitimised. He grumbled, but accepted the issue - though he has informed me that I 'am expected to provide sensible governance to my brother and ensure he remains loyal'. I could hear a silent jab at you through his words Robyn, and it took all my mental strength to not point out how ridiculously long he took to announce his claim on the throne. He only has himself to blame - and maybe the fire witch.

She still keeps sending me those looks and is constantly petitioning to burn down the godswood. Thankfully Stannis isn't that much of an idiot. I do worry that she knows something however, about our communication. Once out of the blue she asked about you: what you were like, what you would have done in certain situations. You should keep an eye of Dragonstone in your world to make sure she doesn't try anything.

But enough about them. Just yesterday we got a raven from the south. Someone calling himself Aegon Targaryen has invaded the Stormlands, laying siege to Storm's End. According to the message he has the word of Jon Connington (the royalist commander from the Battle of the Bells) and the strength of Golden Company behind him. As you probably expect he 'calls on all true and loyal men' to join him. Worryingly, both Stannis and Melisandre think he might actually be the son of Rhaegar; spirited out of the kingdom by a Varys. Obviously no one has pledged allegiance to him here but in the south...the last thing we need here is another claimant, sister.

Robyn, I don't agree with your plans. While I can understand your desire to protect those close to us, what you suggest is far too close to breaking guest right. Combined with the fact that Stannis and Renly haven't done anything in your world - though I do acknowledge the latter's marriage is a threat - it just feels like you're repeating the Lannisters' mistakes sweet sister. Surely there's a better way to go about things, one that doesn't require assassination.

But I will stand behind you if you go down this path. Whatever comes we'll face it together.

Love Jon.

Letter 6 - Robyn

Jon,

The Queen is dead, finally. I was worried the day might never come but at last it has! And no one suspected me for an instant, your suggestion to frame Targaryen loyalists worked like a charm. And the look on her face when she finally realised what was about to happen...

I wish you could have been there, brother. She thought of herself as this great schemer, with myself just as a naive follower to her plans to assassinate the Baratheon brothers (even though I suggested the methods). But with a single nod from me, that vision crashed down around her eyes. She didn't even have a chance for a last curse before her own hired man had slit her throat in two.

For you see brother, the problem with a sellsword or mercenary is that they can be rehired.

I had to kill the hired mercenary myself, of course but as I had seduced him prior to the murder, there was no difficulty in this. And after his blood had fallen on my dress, all that was left to do was scream - content that the letter I'd forced in his pocket would tell the story I wanted.

My boy husband (for he is so much a boy, not like you Jon) was as you expected, devastated by the loss. I suppose I can not blame him, for loosing your parents and two uncles in the span of two months would upset anyone. Though I confess, part of me delights in the shoe being on the other foot now. Do you not like this Lannister? Does it tear at your soul, as it did mine?

His true father is also distressed by his lover's death, but to his mild credit he has done a decent job of hiding it. I've taken him on as my personal guard now, an amusing change from our relationship in the war in your world. He'll be a loyal dog to me, as the hound is still to Joffrey. For after all, the Kingsguard obey the king and the king obeys his queen. Even more so now that his child grows within my womb.

I will have Stark children, brother. Not Lannister or Baratheon or anything else. I hope they look you or me, instead of having blond hair and green eyes. They'll be more our children than his.

According to father, Sandor has finally arrived back at Winterfell where Rodrick, Luwin and mother will attempt to kick the prat into shape. I confess, I'm not sure they will succeed. They'll probably have to stand watch in the bedchamber if my suspicions about his 'fantasies' are accurate. If they are, well - maybe Arry or a second son of mine will have to take Winterfell.

That is of course assuming that Joffrey survives long enough to get another child off me. Don't panic brother, I'd be discreet of course and wait until I have a surviving child. But the death of a boy king would spur the hatred of the Great Houses and that might be necessary if the Targaryens do invade. I've tried to head an invasion off by sending assassins after Daenerys and the boy Aegon, regardless of whether or not he is a trueborn dragon. Varys too has been executed, as punishment for 'treason and assisting in the death of the monarch.' But all is together now and with Margaery Tyrell's child confirmed as heir to Storm's End and Tommen as heir to Casterly Rock, the realm will be secure whatever happens. From an invasion from the east, or one from the north.

I told you I was good, Jon.

Queen Robyn Baratheon

- The End -

Timeline of Events

Red Wedding as Canon.

Letter 1: Robyn has just arrived in King's Landing.

Tourney of the Hand.

Letter 2: Jon's reply to letter 1.

Letter 3: Week before Robyn's marriage.

Robyn marries Joffrey.

Stannis arrives at the Wall, defeats Mance Ryder.

Letter 4: Days after Mance Ryder's Defeat.

Jon accepts Stannis's offer.

Robyn is pregnant and begins to worm her way into Cersei's confidences.

Winterfell is captured by Jon and Stannis, Bolton's driven extinct.

Letter 5: Day after Battle of Winterfell.

Alt-Stannis, Alt-Renly and Alt-Robert assassinated.

Alt-Cersei assassinated, with Targaryen loyalists framed.

Letter 6: Week after Alt-Cersei's death.